1. Field of the Invention
The invention relates to switches for small, hand-held electrical appliances. In particular, the invention relates to waterproof electrical power switches in which the electrical contacts are hermetically sealed. Even more particularly, the invention relates to magnetically operated electrical power switches.
2. Description of the Prior Art
Hand-held hair dryers and similar small electrical appliances are often used in environments creating some risk that the appliances will come into contact with water thereby creating the danger of electrocution or serious shock to the user. These dangers exist with respect to A.C. powered appliances whether or not the power switch of the appliance is on or off because of the presence of electrical potential on the conductive parts within the appliance. The use of a double pole waterproof switch eliminates these dangers when the appliance is turned off, but such switches are difficult to manufacture within all of the constraints dictated by the environment in which these switches must be used.
Some prior art shock hazard protectors are known which shut off power to the appliance when it comes into contact with water. These devices generally have two main features; a sensor means to sense the danger causing condition and an actuator means to rapidly open the power lines. U.S. Pat. No. 4,464,582, for example, shows an automatic power shut-off circuit which utilizes a pair of flexible metallic conductors spaced apart a predetermined distance and secured to an electrical appliance in a labyrinthine pattern. When water bridges the space, the circuit energizes a solenoid to open a pair of switches in the power line to the appliance. Both sensing and actuation portions of this device are too costly and complex to be incorporated in relatively low cost electrical appliances.
Another type of shock hazard protector is shown in U.S. Pat. No. 4,589,047 (Gaus). The sensor part of the device shown in this application is a two-wire circuit arranged at the edges of openings and joints through which water may penetrate. The device also includes triac having a circuit responsive to the sensor. The actuator part of the device is a self-opening mechanical switch which is normally held closed by a fusible wire which is melted upon the firing of the triac. The actuator part of this device is complex and relatively costly for use in small appliances. The sensor part of this device requires several circuit components and must be triggered by a water bridge across the two-wire circuit. The sensor is, therefore, also relatively costly.
The complexity of the aforementioned patents results because the devices are intended to turn power off to the small appliance when water bridges a pair of sensor wires before it touches any high voltage parts of the appliance. The complexity and high cost of these devices inhibits their use in small appliances.
Accordingly, there is a need for a safe shock hazard protector which is sufficiently inexpensive so that it may be included in relatively low cost appliances such as hair dryers, curling irons, and the like.
In certain small appliances, it is desirable to provide some electrical protection for the user without the attendant cost and complexity of the foregoing devices. As a minimum, therefore, it is desirable to provide a means by which electrical power could be absolutely insulated within an electrical appliance until its use. As mentioned above, hermetically sealed waterproof power switches have been used in some prior art applications with some success. However, in certain small hand-held appliances such as hair dryers, the necessary size of such switches and the physical constraints within the hair dryers prohibit the use of available waterproof switches. Additionally, hair dryers very often have a plurality of power settings, for example, "off", "low", "medium", "high" and providing a totally waterproof switch capable of operating in all these modes has not heretofore been possible.
It is known to use magnetic reed switches in hermetically sealed containers. U.S. Pat. No. 1,958,482 (Leins), for example, shows a glass container enclosing a stationary electrical contact and a movable electrical contact attached to the end of a flexible cantilevered spring member which has an armature secured thereto. An external magnet may be moved in close proximity to the casing to attract the armature and thereby close the switch. While such an arrangement might be suitable for some appliances, all known small magnetic switches are relatively unstable for use in environments such as small hand-held appliances which are subject to being dropped or roughly handled because the switches may tend to open or close unpredictably.
It is accordingly an object of this invention to provide a waterproof switch capable of eliminating any possible exposure of live electrical parts of a hair appliance to water unless the power switch is on.